Proposal to require a vehicle stability function on vehicles with four axles commercial vehicles over 25 tons in light of their specific use.

Text prepared by the GRVA secretary, based on GRVA/2023/2 as adopted by GRVA during the 15th session, to highlight amendments to the approval number and marking provisions with regard to the series of amendments.

Proposal to add the text, "In case that saturation of the front tyres happens before the above calculated magnitude angle, this angle may be used as the final steering amplitude, but only if this angle is greater or equal to 6.5 A.” based on the following justification:

1. Reaching fixed amplitude, i.e., fixed steering wheel angular speed due to given 0.7 Hz sine frequency, needs much more torque with quick steering gear ratio systems than with slow steering gear ratio systems, and produces much more wheel steer.
2. Car behavior (yaw rate, lateral acceleration and thus trajectory) is similar for all amplitudes above approx. 7 to 8 A (i.e., more than 7 times the steering wheel angle corresponding to 0.3 g), because front tires are saturated. More steer of the tires doesn’t provide more lateral force, so yaw rate and lateral acceleration don’t increase. Continuing to increase steering wheel amplitude after front tire saturation doesn’t give more information.
3. There might appear in the future some vehicles which have significantly low steering gear ratio (i.e., quick steering characteristics) and may need too much steering wheel torque to achieve the 270 degrees sine amplitude at 0.7 Hz (not reachable by conventional steering robots), then jeopardizing the easy approval of future beneficial steering equipment e.g. steering-by-wire systems.